The invention concerns an open end spinning frame with a plurality of spinning assemblies disposed side by side, which assemblies have a monitoring yarn sensor in the zone of the yarn takeoff passage that senses the presence of a yarn, said yarn sensor having a magnet, associated with which there is a stationary electromagnetic switch for switching on or off a device for sliver supply to the spinning assembly in question, in dependence upon the position of the yarn sensor, whereby an auxiliary magnet for switching on the sliver feed for a piecing process can be presented to the said magnetic switch.
In open end spinning assemblies it is customary to have arrangements whereby the sliver feed will be interrupted if there is a yarn break. For a piecing process, the sliver feed must again be switched on after a specific time interval, so that there will be a ring of sliver present in the spinning rotor to which yarn can be applied in piecing.
It is known (German AS No. 2,012,108) that a swingable yarn sensor may be provided for the spinning assemblies of an open end spinning frame, in the region of the yarn takeoff passage, said sensor having a magnet with which an electromagnetic switch is associated. With a break in the yarn, the yarn sensor swings into an inoperative position whereby its magnet moves away from the magnetic switch, opening the switch and interrupting the sliver feed. In this construction, a mobile device is provided for the open end spinning frame, from which the piecing operation is executed. The device has a transfer clamp disposed so as to be swingable by 180.degree. about a vertical axis, which brings a yarn end over the opening of the yarn takeoff passage. For piecing, the yarn is then carried back into the spinning rotor, applied there to a ring of sliver and then drawn off again. In order to produce a sliver ring in the spinning rotor, there has to be correctly timed switching on of the sliver feed. In the known construction this is effected by means of an auxiliary magnet that replaces the magnetic field of the magnet connected with the yarn sensor in the region of the magnetic switch and switches on the sliver feed. In the known construction the yarn is introduced during the piecing in such a way that it lies on the wrong side of the yarn sensor, because the yarn sensor is still in its switched off position. After the piecing, the running yarn is deflected by means supplementary to the transfer clamp, in such a way that it is carried around the yarn sensor and moves to the correct side. Accordingly the yarn presses the sensor into its operative position, so that the yarn sensor magnet is opposite the magnetic switch and holds the sliver feed switched on until another yarn break occurs. The transfer of the running yarn to the other side of the yarn monitor requires expensive construction. Besides, the time spent by the piecing device at the spinning assembly in question is prolonged, which as a whole has a poor effect on the economy of the device.
The invention is addressed to the problem of producing an open end spinning frame of the indicated type in such a way that a yarn will be applied on the correct side of the yarn sensor in piecing, without thereby limiting the functioning efficiency of the piecing operation. An important feature of the invention is the provision that the auxiliary magnet is disposed so that it may be moved to the magnet of the yarn sensor which is in the switched off position, the poles of the said magnets having the same polarity.
By this arrangement, the auxiliary magnet will exert a force on the yarn sensor magnet, whereby the yarn sensor will be brought into its operational position. In spite of this switchover of the yarn sensor, the sliver feed will not yet be switched on, because its control is then assumed by the auxiliary magnet, which is presented to the magnetic switch.
In an advantageous embodiment of the invention, it is provided that a stationary magnet with its poles disposed in opposition will be associated with the yarn sensor magnet, which stationary magnet draws the yarn sensor to the running yarn. The stationary magnet is thereby so disposed that yarn tension can then hold the yarn sensor against magnetic forces, in the position of operation. If there is a yarn break, the magnet of the yarn sensor will then be attracted to the stationary magnet, whereby then the forces acting between the two magnets will increase strongly as the distance is reduced.
In an advantageous embodiment of the invention, it is provided that the action of the auxiliary magnet presented to the yarn sensor magnet and to the magnetic switch can be varied according to its presentation. Here use is made of the situation that only minor magnetic forces are required to hold the yarn sensor magnet in the operating position because it is relatively remote from the magnet that is associated with it. The magnetic field of the auxiliary magnet can therefore be reduced in this position, without the yarn sensor thereby being moved out of its operating position. The reduction of the magnetic field may be such that thereby the magnetic switch will open and thus the sliver feed will be controlled. This allows the further advantage that during piecing the sliver feed can be simply controlled with respect to quantity, which is a special advantage in automatic piecing because thereby the quality and appearance of the pieced place can clearly be improved.
These and other objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, a single embodiment in accordance with the present invention.